There have been investigated many high molecular substances, for example, natural polysaccharides such as cellulose, starch, amylose, dextran, pullulan, carrageenan, alginic acid, mannnan, agarose, locust bean gum, xanthan gum, chitin, chitosan, etc.; and proteins such as collagen, gelatin, casein, peptide, etc., and their chemically modified products as materials of shaped products such as edible films, sheets, capsules, etc.
Particularly, water-soluble edible films have been produced from starches and polysaccharides derived from starch as materials. The typical example is a cachet. However, since such a cachet has a relatively low moisture-retaining property and resistance to humidity, and has a fragility and low transparency, the applicability of cachet have been restricted. To improve these disadvantages, the use of amylose films, which are produced by using natural amylose separated from starch, amylose obtained by hydrolyzing starch with starch-debranching enzymes, or high-amylose-starch with a high amylose content, was proposed. The films have a relatively high strength, plasticity, no oxygen-permeability, and resistance to oil. However, the amylose films are unsatisfactory in transparency and not dissolved completely even in hot water because of their low solubility. Further, the amylose films have a relatively low moisture-retaining property and resistance to humidity, and have the disadvantages of causing adhesion by absorbing moisture, causing a retrogradation of amylose during the preservation, and being fragile by drying because the films are susceptible to atmospheric humidity. Therefore, the amylose films have not been practically used.
Recently, to improve the disadvantages of starch films and amylose films, pullulan films, one of HPCS, are produced from a water-soluble natural polysaccharide, pullulan produced by Aureobasidium pullulans. As disclosed in “Tennen-Kobunshi-no-Saishin-Riyoh-Gijutsu (The latest technique using natural macromolecules)”, pp. 145-155, edited by CMC publisher, Tokyo, Japan, 1982, pullulan films are colorless, transparent, tasteless, and odorless, and have a relatively high solubility in water as compared with starch films or amylose films, and a satisfactory gloss and transparency. Also, pullulan films have a satisfactory printing property and an aspect as a low-caloric food because pullulan is hardly digested by living bodies.
Although capsules can be produced from pullulan, they have been produced using gelatin as a main material. Recently, however, there is a trend that ingredients originated from animals such as gelatin are not preferable because of fear of the pollution by infectious diseases of domestic animals such as bovine spongiform encephalopathy (BSE) and foot-and-mouth disease (FMD). Therefore, it is expected to provide capsules using pullulan as a main material.
Although HPCS has highly useful features as described above, it has a serious disadvantage of being easily affected by the change of humidity. HPCS easily releases moisture under a low humidity condition to affect elasticity. Although glycerin, sugar alcohol, etc. have been conventionally used as plasticizers to improve the disadvantages of HPCS, HPCS prepared with those have disadvantages of absorbing moisture easily and causing adhesion under a high humidity condition.